There're two ways to mod Voxel Tycoon experience:
Content mod is a set of configuration files, models, and other content which is processed by the game.
The game should know how to process these files, so content mods always use already existing behaviours and mechanics provided by the game.
Script mod is a full-featured program. Contrary to content mods, you can create new behaviours and mechanics with script mods, as well as extending or modifing existing ones.